1. Field of the Invention
The present invention relates to an adaptive coding and modulation (ACM) apparatus and method for a forward link in satellite communication, and more particularly, to a technology that may reduce a system load by executing a channel prediction algorithm only when a signal-to-noise ratio (SNR) of a received signal is less than or equal to a threshold value (SNR_TH), taking a load of an adaptive coding and modulation controller into account.
2. Description of the Related Art
Currently, satellite communication through which a telephone service is provided to subscribers located in remote areas is being widely used.
Satellite communication implements a long distance communication using an artificial satellite outside of the atmosphere as a relay station.
Satellite communication increases a service coverage area and ensures ultra-high speed transmission using high-frequency electric waves. One of the types of satellites being used is a geostationary satellite in which has a geostationary orbit, with an orbital period that is the same as the rotation period of the Earth. A geostationary satellite has a property of remaining permanently fixed in exactly the same position in the sky. Such a satellite is often used for satellite communication purposes.
According to the characteristics of microwaves, satellite communication allows a high-speed, large-capacity communication and a wide service coverage area, for example, an entire region of a predetermined country.
Also, satellite communication ensures reliability of communication irrespective of topography, and is robust against a disaster. However, because a travel time of electric waves, for example, about 0.24 seconds, disadvantages in terms of a propagation delay and a lack of data security are present in voice communication.
Due to use of a solar cell as a power source, satellite communication may experience a temporary loss of communication when a satellite passes into the shadow of the Earth or during heavy rain.
However, a separate signal line for communication in shortwave bands or higher passing through the ionosphere is not required for satellite communication, and thus is available for a transcontinental long-distance communication or communication in a country with mountainous areas.
Accordingly, satellite communication is being beneficially used for international communication, domestic long-distance communication, maritime communication, aeronautical communication, and the like.
Initially, applications of satellite communication faced limitations with regard to international telecommunications or television (TV) broadcasting due to a high cost of a satellite, but with technological advancements and cost reductions, satellite communication has been extended to various types of applications, for example, data communication, remote data gathering, personal computer (PC) communication, Internet communication, cable TV (CATV)/video distribution, distance education, intra-company communication, leased lines, videoconferencing, newspaper transmission, satellite news gathering (SNG), broadcasting of various events, and the like.
A conventional continuous coding and modulation (CCM) standard, digital video broadcasting satellite second generation (DVB-S2), uses a coding scheme and a modulation scheme selected for a predetermined availability unchangeably throughout a service coverage area. This CCM scheme needs to maintain a high margin in accordance with system availability standards, even under clear sky conditions.
In a case in which a CCM mode is applied to satellite communication, when rain attenuation is severe, attenuation of the entire satellite link may increase, resulting in discontinuity of the link. An adaptive coding and modulation (ACM) may increase an average system throughput and availability.